Recent investigations have shown a direct relationship between increasing severity of chronic periodontitis and the proportions of oral spirochetes in the subgingival periodontal flora in man. In certain forms of periodontal disease oral spirochetes can be shown to actually invade the gingival tissues. Since cultivation of oral spirochetes is difficult, little is known about their physiological, biochemical or serological properties, or their interaction with periodontal tissues. We are proposing (1) to evaluate the prevalence of oral spirochetes in the subgingival area of human subjects with selected periodontal conditions, (2) to compare circulating antibody titers in the same groups of subjects to four strains of oral spirochetes currently growing in our laboratory, (3) to determine the effect of periodontal treatment on the prevalence of oral spirochetes in the subgingival area of patients with gingivitis and chronic periodontitis and, simultaneously, to measure circulating antibody titers to four strains of oral spirochetes and, (4) to adapt techniques currently in use in our laboratory to the immunological labeling of spirochetes or their structural constituents in pure cultures and in oral tissues. Prevalence of spirochetes will be estimated on a proportional basis by differential dark field microscopic examination of subgingival scrapings. Circulating antibody titers will be determined by an enzyme-linked immunosorbent assay (ELISA) and an indirect fluorescent antibody (IFA) technique, using whole cells or a cell sonicate as the test antigen. Labeling of spirochetes or their products in tissues will be done in tissue sections by using two different techniques, one in which the labeling procedure is carried out on ultrathin sections and one in which thick sections are labeled prior to embedding for ultrathin sectioning. The techniques will be tested by injecting whole cells or sonicated extract into the palatal tissue of laboratory rats. Eventually, the results may be applicable for studies of biopsied human gingiva obtained during surgical therapy from patients with chronic periodontitis and acute necrotizing ulcerative gingivitis (NUG).